diff --git a/sys/kern/kern_umtx.c b/sys/kern/kern_umtx.c
index cf472912164b..a40aa5a358c8 100644
--- a/sys/kern/kern_umtx.c
+++ b/sys/kern/kern_umtx.c
@@ -820,8 +820,8 @@ umtx_key_get(const void *addr, int type, int share, struct umtx_key *key)
 		    (share == AUTO_SHARE &&
 		     VM_INHERIT_SHARE == entry->inheritance)) {
 			key->shared = 1;
-			key->info.shared.offset = entry->offset + entry->start -
-				(vm_offset_t)addr;
+			key->info.shared.offset = (vm_offset_t)addr -
+			    entry->start + entry->offset;
 			vm_object_reference(key->info.shared.object);
 		} else {
 			key->shared = 0;